The present invention relates to a support body for an apparatus having an extended nip defined by a contact surface of the support body and an opposed surface, wherein the support body                has two side surfaces facing from each other and connecting to the contact surface, and a bottom surface facing from the contact surface, and        is arranged to be moved in the direction towards the opposite surface by means of a loading system in order to load the nip via the contact surface.        
The invention also relates to a holding device for such a support body.
The invention further relates to an apparatus/press for the treatment of a fiber web that is manufactured in a paper or board machine, comprising a first structural element and a second structural element which is movably arranged and having an opposite surface for interaction with the first structural element while forming an extended nip, the first structural element comprising a movable clothing and a support body/press body having a contact surface/press surface that defines the nip together with the opposite surface, wherein the support body/press body                has two side surfaces facing from each other and connecting to the contact surface/press surface, and a bottom surface facing from the contact surface/press surface, and        is arranged to be moved in the direction towards the opposite surface by means of a loading system in order to load the nip via the contact surface/press surface.        
The invention also relates to a method of forming an extended nip in an apparatus that comprises the support body.
The invention also relates to a method of controlling the load in an extended nip in an apparatus that comprises the support body.
The previously known presses with an extended press nip have a so-called press shoe, which consists of a metallic material such as aluminium or steel, and are designed with a press surface, usually a concave press surface, whose profile is very accurately adapted to the opposed counter-pressure surface. Such a press shoe is very complicated to manufacture and therefore involves a very high cost. Because it consists of metal, it is relatively rigid and inflexible. The press roll acting as a counter roll of such a shoe press can have a relatively thick cylinder wall that withstands the forces from the press shoe. In accordance with another embodiment of the counter roll, it has a relatively thin cylinder wall and is provided internally with a counter pressure system for adjustable crowning of the thin, and thus deformable, cylinder wall or shell in dependence of the forces the press shoe has to apply on the counter roll in order to obtain the desired load. Also the press shoe can be crowned in accordance with the crowning of the counter roll, and it will then be usable only in combination with this counter roll. Alternatively, the metallic press shoe can be tilted by means of hydraulic cylinders.
A Yankee cylinder has a cylinder wall or shell that is relatively thin and that easily is deformed by impression of the press shoe when the Yankee cylinder is used as a counter roll. The deformation of the shell varies in an axial direction from the central region in a direction towards the end walls, where the impression is substantially smaller than within the central region. Therefore, the press shoe will act with a higher pressure at and in the vicinity of the end walls, resulting in an increased wear at the edges of the press felt and an irregular load profile along the press shoe, which in its turn results in variable paper properties crosswise to the machine direction. It has been proposed to crown the shell of the Yankee cylinder by means of an internal counter-pressure system, or to arrange two or more rows of hydraulic cylinders on the underside of the press shoe for influencing the press shoe to conform to the deformed surface, in both cases in order to achieve a more uniform load profile. Both proposals, however, are complicated and expensive to carry out.
The following documents are examples of presses having extended press nips.
DE 44 05 587 and WO 02/44467 describe a press having a hydrostatic bearing, including a press shoe 3 or double press shoes 3a, 3b of the same design. A press belt 6 rotates on top of a lubricating fluid bed of the press shoe 3 with a very small friction. The press shoe, which is made of metal, has a pressure chamber 10 containing a hydraulic fluid, preferably water. A rectangular pressure-equalizing membrane 20, consisting of a suitable solid material, preferably stainless steel, is fixed on the press nip side of the press shoe. The pressure-equalizing membrane 20 has an outer edge 26, an inner edge 22, and an opening 27 that is defined by the inner edge 22. The pressure-equalizing membrane 20, thus looking like a frame, is flexible so that an edge zone 21, standing in direct contact with the hydraulic fluid, can deflect when pressure differences occur between its two sides. These pressure differences arise when hydraulic fluid happens to leak out through the press nip as a result of irregularities in the paper web and/or in the envelope surface of the counter roll. Thus, the flexible pressure-equalizing membrane 20 creates a self-adjusting nip 2 having no or only a minimum of fluid leakage. Thus, through the opening 27 in the pressure-equalizing membrane 20, the pressure fluid in the pressure chamber 10 stands in direct contact with the movable belt. The complementary addition that has been done in the WO-publication in comparison to the DE-publication is that the flexible membrane has been provided with “pinholes 25” within its free edge zone 21 in order to conduct hydraulic fluid from the pressure chamber 10 to the belt 6 for the purpose of lubricating the belt.
U.S. Pat. No. 5,980,693 describes presses having a tube-shaped or inflatable loading element, but with a metal shoe between the loading element and the inside of the belt. Furthermore, this part of the shoe is constructed in order to provide a slow reduction of the pressure in the nip outlet. Normally, an abrupt pressure drop is desired.
U.S. Pat. No. 3,839,147 describes a shoe press having two opposed shoes. Each shoe has a metal bottom and sills, sealing against the inside of the belt. The side of the shoe facing the belt is a perforated diaphragm, which causes the pressure of the hydraulic fluid in a pressure chamber to load the inside of the belt directly. The shoe is of a rather complicated construction with various apertures and reinforcements.
U.S. Pat. No. 5,951,824 describes an ordinary shoe having ordinary hydraulic loading elements. The shoe is coated with a soft and durable layer of polymer or rubber in order to reduce the risk of damages to the belt and shoe from paper wads passing through the press nip.
EP 0 575 353 describes a press having a shoe, which is loaded with bellows arranged inside a metal cover of the shoe, wherein a belt slides around the metal cover.
U.S. Pat. No. 6,334,933 describes a press having a counterpart of metal, which is provided with a plurality of pressure pockets sealed by a metal plate and hoses, which also can contribute to loading the opposite portions of the press nip.
U.S. Pat. No. 6,387,216 describes a press having an open fluid chamber, over which a belt is running and which is loading the press nip. The chamber is sealed by means of setting the belt under pressure, so that it is tightened over the edges of the chamber.
EP 1 319 744 describes a method for measuring and regulating the nip pressure in a shoe press, crosswise to and along the web, by means of measuring and continuously adapting the hydraulic static pressure in reference points above measurement holes in the press nip.
DE 30 30 233 describes an elastic slide shoe that is attached to a stand of metal. The slide shoe includes a solid body or a hollow body in the form of a hose that can be filled with a pressure medium. The hose is surrounded by an elastic belt that is attached to the metal stand. The hollow body may be divided into chambers that can be pressurized to different pressures. However, a change of pressure in the chamber or chambers does not result in a change of the loading in the nip because of the fact that the hollow body is permitted to expand laterally during every such increase of pressure.
U.S. Pat. No. 4,576,682 describes a press with a shoe consisting of two shoe parts each of which being able to load the nip in a hydrodynamic manner.
U.S. Pat. No. 4,568,423 describes a press with a shoe having a shoe part in the form of a hydrostatic chamber, and two further shoe parts having hydrodynamic press function, the further shoe parts also sealing the hydrostatic shoe part.